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gns3-server/gns3dms/modules/daemon.py

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"""Generic linux daemon base class for python 3.x."""
import sys, os, time, atexit, signal
class daemon:
"""A generic daemon class.
Usage: subclass the daemon class and override the run() method."""
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def __init__(self, pidfile, options):
self.pidfile = pidfile
self.options = options
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def daemonize(self):
"""Deamonize class. UNIX double fork mechanism."""
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try:
pid = os.fork()
if pid > 0:
# exit first parent
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sys.exit(0)
except OSError as err:
sys.stderr.write('fork #1 failed: {0}\n'.format(err))
sys.exit(1)
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# decouple from parent environment
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os.chdir('/')
os.setsid()
os.umask(0)
# do second fork
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try:
pid = os.fork()
if pid > 0:
# exit from second parent
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sys.exit(0)
except OSError as err:
sys.stderr.write('fork #2 failed: {0}\n'.format(err))
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sys.exit(1)
# redirect standard file descriptors
sys.stdout.flush()
sys.stderr.flush()
si = open(os.devnull, 'r')
so = open(os.devnull, 'a+')
se = open(os.devnull, 'a+')
os.dup2(si.fileno(), sys.stdin.fileno())
os.dup2(so.fileno(), sys.stdout.fileno())
os.dup2(se.fileno(), sys.stderr.fileno())
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# write pidfile
atexit.register(self.delpid)
pid = str(os.getpid())
with open(self.pidfile,'w+') as f:
f.write(pid + '\n')
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def delpid(self):
os.remove(self.pidfile)
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def check_pid(self, pid):
""" Check For the existence of a unix pid. """
try:
os.kill(pid, 0)
except OSError:
return False
else:
return True
def start(self):
"""Start the daemon."""
# Check for a pidfile to see if the daemon already runs
try:
with open(self.pidfile,'r') as pf:
pid = int(pf.read().strip())
except IOError:
pid = None
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if pid:
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pid_exist = self.check_pid(pid)
if pid_exist:
message = "Already running: %s\n" % (pid)
sys.stderr.write(message)
sys.exit(1)
else:
message = "pidfile {0} already exist. " + \
"but process is dead\n"
sys.stderr.write(message.format(self.pidfile))
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# Start the daemon
self.daemonize()
self.run()
def stop(self):
"""Stop the daemon."""
# Get the pid from the pidfile
try:
with open(self.pidfile,'r') as pf:
pid = int(pf.read().strip())
except IOError:
pid = None
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if not pid:
message = "pidfile {0} does not exist. " + \
"Daemon not running?\n"
sys.stderr.write(message.format(self.pidfile))
return # not an error in a restart
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# Try killing the daemon process
try:
while 1:
os.kill(pid, signal.SIGTERM)
time.sleep(0.1)
except OSError as err:
e = str(err.args)
if e.find("No such process") > 0:
if os.path.exists(self.pidfile):
os.remove(self.pidfile)
else:
print (str(err.args))
sys.exit(1)
def restart(self):
"""Restart the daemon."""
self.stop()
self.start()
def run(self):
"""You should override this method when you subclass Daemon.
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It will be called after the process has been daemonized by
start() or restart()."""